For many years rotary shear valves have been used in pressurized fluid instruments for fluid switching, sample injection, fraction collection, stream sampling, solvent selection and fluid redirection. In the field of HPLC most conventional applications operate in the 1,000 psig to 6,000 psig high pressure domain. Only in the last few years have HPLC pressures increased up to 20,000 psig in order to reduce analysis time and increase performance. By comparison, DNA Sequencing and In-vitro diagnostic instruments in general operate at much lower pressures, from vacuum to positive pressures in the range −10 psig to 200 psig.
With regard to fluid flow control, rotary shear valves are commonly selected for a number of reasons including accuracy, precision, repeatability, reliability, chemical compatibility, ease of automation, relatively long wear and low cost. One of the primary functions of the shear valve is to create a fluidic seal, where leak rate is limited from 0.3 μL/min to 1 μL/min maximum, in order to prevent loss of sample, solvent or other pressurized fluid and achieve precision, accuracy and instrument performance. Of equal importance is the ability to direct fluid from one location to another for sample analysis, solvent selection, purging and other fluidic functions.
The means for creating a nearly leak tight seal is to apply an axial force causing a rotor element and stator element to come into contact by compression. The force created can range from 30 lbf to 800 lbf depending on the application. Most if not all rotary valves apply the compression force by means of springs, such as helical, belleville or clover. Accompanied with these components are additional parts such as washers, adjusting nuts, guides, shims and threaded features. An example of conventional loading methods is found in FIG. 3 of U.S. Pat. No. 8,622,086 where a helical spring is shown contained in an adapter component which rides on ball bearings and also positions and pushes a rotor seal against a stator seal. Another example is described in FIG. 1B of US patent application No. 2014/0191146 showing a conventional method that uses a minimum of 12 parts including 4 springs, 3 washers, spacer, thrust bearing, bearing washers and shims.
Accordingly, it is desirable to provide a low pressure micro-fluidic valve assembly that significantly reduces the part quantity by eliminating a primary element, namely the conventional spring assembly described above.